1. Field of the Invention
The present invention relates to a method and apparatus for detecting and controlling a beam current of a cathode ray tube, through detection and control of a clamp current of the cathode ray tube, which is representative of the beam current.
2. Description of the Related Art
Cathode ray tubes ("CRT") are typically employed in electronic display systems, such as a television receiver or a display apparatus including a CRT numerical display. In such electronic display systems, luminance or brightness control is typically desired. Luminance indicates the amount of light intensity which is perceived by the eye as brightness. Such luminance control is also termed "white balance" since white light may be considered and provided as a mixture of the red, green and blue primary colors in the proper proportions.
In CRTs, drift characteristics due to aging result in image luminance distortion or the alteration of the white balance. One attempted approach to solving this problem includes the detection and use of the beam current from the CRT driver circuit to control the luminance of the display system. However, since the signal level of the beam current is very small (typically in the order of 10-20 .mu.A), it is difficult to detect. As a result, use of the beam current in controlling luminance is unreliable. In the same manner, use of the beam current in controlling any video signal parameter, is unreliable.
Accordingly, there is a need in the technology for a method and apparatus for a reliable control system for detecting and controlling a beam current of a cathode ray tube in a display system, so as to accurately control a video signal parameter.